Oxygenator



April 25, 1961 DE WALL 2,981,253

OXYGENATOR Filed July 17, 1957 INVENTORS RICHARD/4. DEMLL BY (2nRs/vcsmz ro/vl/ums/ 147- TORNE Y5 OXYGENATOR Richard A. De Wall,Minneapolis, and Clarence Walton Lillehei, St. Paul, Minn., assignors toThe Regents of the University of Minnesota, Minneapoiis, Minn, acorporation of lilinnesota Filed July 17, 1957, Ser. No. 672,438 11Claims. (Cl. 128214) This invention relates to an oxygenating system foruse in an extra corporeal circulation device for temporarily assuming orassisting the functions of the heart and lungs in a human being or otheranimal. More particularly this invention relates to a simple disposabledevice for filming blood for oxygenation and release of carbon dioxideoutside of the body of a human or other animal during cardiac surgery.The oxygenating device of this invention, which temporarily assumes thefunctions of the lungs, is used with a standard blood pump whichtemporarily assumes the function of the heart by circulating the bloodthrough the oxygenator.

The desirability and necessity of temporarily relieving the heart of itsnormal function of pumping blood during cardiac surgery have long beenrecognized and the con cept of extracorporeal circulation is generallyold in the art. In our Patent No. 2,854,002, issued September 30, 1958,from copending application Serial No. 656,175, filed April 22, 1957,which in turn is a continuation of our application Serial No. 598,284,filed July 18, 1956, now Patent 2,898,568, there is described andclaimed a simple inexpensive disposable artificial oxygenator and themethod of oxygenating blood by the use of that device. According to themethod of our earlier application oxygen is introduced into venous bloodfrom a patient by directly dispersing bubbles of oxygen in a column ofblood, the mixed blood and oxygen is discharged into a debubblingchamber provided with a coating of anti-foam agent to dissipate the gasbubbles in the blood, and the oxygenated blood is permitted to flowdownwardly by gravity in a slow laminar flow whereby heavier gas-freeblood is permitted to flow beneath and continuously displace upwardlygas-containing blood of lesser density to insure liberation of entrainedgas bubbles before return of the oxygenated blood to the patient.

The oxygenator, according to the present invention, utilizes the samepumping apparatus and receives and returns the blood in substantiallythe same manner described in our previous applications. Oxygenation,according to the present invention, is accomplished however by a filmingtechnique; that is, by maintaining a continuous film of flowing bloodand exposing that film to an atmosphere of pure oxygen.

It is the principal object of this invention to provide a simple,economical, disposable, film oxygenating and carbon dioxide releasingdevice for use in direct vision intracardiac surgery.

Other objects of the invention will become apparent as the descriptionproceeds.

To the accomplishment of the foregoing and related ends, this inventiont-hen comprises the features hereinafter fully described andparticularly pointed out in the claims, the following descriptionsetting forth in detail certain illustrative embodiments of theinvention, these being indicative, however, of but a fewof the variousways in which the principles of the invention may be employed.

- The invention is illustrated by the drawings in which 2,981,253Patented Apr. 25, 1961 the same numerals refer to corresponding partsand in which:

Figure l is an elevation of the film oxygenator according to thisinvention shown with the front surface partly broken away to reveal theinner construction;

Figure 2 is a transverse, horizontal section taken on the line 2-2 ofFigure 1 and in the direction of the arrows, showing in greater detailthe construction of this disposable film oxygenator; and

Figure 3 is a transverse, vertical section taken on the line 33 ofFigure 1 and in the direction of the arrows, to illustrate in detail theconstruction of the oxygenator.

Referring to the drawings, the oxygenator of this invention includes agenerally rectangular plastic film envelope indicated generally at 10,having a front face film panel 11 and a back face film panel 12. The topof the oxygenator is provided with hanging means in the form of anelongated loop 13 of plastic film extending across the top of theoxygenator and adapted to receive the rod 14 of any suitable supportingand tensioning rack. Similarly, the bottom of the oxygenator envelope 18is provided with an elongated loop member 15 adapted to receive the rod16 of the supporting rack. The opposite side edges of the oxygenator areprovided with loop members 17 and 19 respectively, adapted to receiverods 18 and 20 respectively. The interior of the plastic envelope 10includes a pair of foraminous filming elements here shown as fine meshscreen members 21 and 22 disposed between the front and back face filmpanels of the plastic envelope.

The screens 21 and 22 are held spaced apart in order to provide a thinchannel 23 for the how of blood through the oxygenator. According to theillustrated form of construction, the opposed marginal edge portions ofthe side loop member 17 are sealed to a spacer 24 of appropriatethickness such that the total thickness corresponds to thedesired-spacing between the screens. Similarly, the op posed marginaledge portions of the loop member 19 are sealed to a spacer 25 and theopposed marginal edge portions of loop member 13 are sealed to a spacer26. The marginal edges of screen members 21 and 22 are stitched or heatsealed or otherwise secured to the opposite sides of the compositespacers thus produced. The composite spacer along one side edge of thepair of oxygenator screens is made somewhat wider and is provided with aplurality of openings 27 adjacent to the edge of the pair of screens forpassage of gas from one side of the envelope to the other for a purposehereafter explained.

A manifold tube 28 is disposed between the screen members 21 and 22 atthe top of the oxygenator. The manifold 28 is in the form of a plastictube provided with a stopper 29 closing one end and a stopper 30 fittedwith a blood inlet tube 31 at the other end. The manifold 28 is providedwith a plurality of small openings 32 along its bottom surface for flowof blood between the screens and a few vent openings 33 along itstopsurface. Optionally, the manifold is also provided with a fine meshfilter 34- in the form of a V-shaped trough below the bottom of themanifold tube.

Because the thickness of the manifold 28 tends to separate the screenmembers 21 and 22 spacer elements 35 and 36 extending the width of thescreens are provided between the screen members on opposite sides of thedepending portion of the filter element 34. This provides formaintaining the spacing of the screened members 21 and 22 substantiallythe same at the top as along the side edges. In order to maintain thespacerelements 35 and 36 in place Without choking off the flow of bloodthrough the filter the spacers are spot-stitched or otherwise secured tothe screen members at a plurality of points,

indicated at 37, across the width of the screens. The

provided with similar spacers to hold the screens apart without shuttingoff the flow of blood between the screen members, although in mostinstances this precaution is not necessary at the bottom of theoxygenator.

The front and back face panels of the oxygenator envelope are appliedover the screen and sealed to the opposite inside marginal portions ofthe loop members. Blood inlet tube 31 is sealed between the panels. Oneface panel is provided with an oxygen inlet tube 38 sealed into thepanel and the opposite face panel is provided with a similar gasdischarge tube 39 sealed into that panel. Both the oxygen. inlet tube 38and the gas vent 39 are disposed generally along the side edge oppositeto that containing the gas passage openings 27 and intermediate of thetop and the bottom of the screen members. The front panel 11 and thescreen member 21 define a space between them into which oxygen isintroduced from the oxygen inlet 38. Similarly, the back panel 12 andscreen 22 define a space 41 into which carbon dioxide is released fromthe blood and excess oxygen from the space 40 passes through ventopenings 27 to the discharge outlet 39.

The face panels 11 and 12 are sealed together at the bottom so as toform a reservoir 42 for collecting oxygenated blood for return to thepatient through a blood outlet tube 43 sealed between the film panels.The reservoir 42 and blood outlet 43 may be disposed centrally in thebottom of the oxy-genator envelope, but, desirably, they are offset toone side as illustrated in the preferred embodiment of the oxygenatorshown in Figure 1 wherein an inclined passage 44 is. formed between thesealed surfaces of the panels. The inclined passage 44 is an addedprecautionary measure. As blood flows from between the screens 21 and 22at the bottom of the oxygenator, means is thus provided for laminar flowwhereby heavier gas-free blood is permitted to flow beneath and displaceupwardly any gas-containing blood of lesser density, if such be present.A vertical gas escape tube 45 communicating with the upper portion ofthe offset blood reservoir 42 is sealed between the panels and the frontpanel 11 is split adjacent the upper end of tube 45 to permit escape ofgas to the atmosphere.

The film oxygenator of this invention is designed to be efficient whileat the same time being simple, economical and disposable. The oxygenatorenvelope and its supporting loops are formed from a continuous,impervious, plastic film, such as for example: polyethylene, plasticizedpolyvinyl chloride, vinylidene chloride polymers, tetra fluoroethylcnepolymers, trifiuorochloroethylene polymers, rubber hydrochloride and thelike. The plastic films should be pure, nontoxic, strong, preferably atleast partially transparent and capable of being sterilized. Preferably,the synthetic resin films should also be heat scalable for ease inmanufacture of the oxygenator.

The screen members 21 and 22 must be of fine mesh, non-wettable byblood, and, of course, pure, non-toxic, strong and capable of undergoingsterilization. screens are desirably woven and many suitable syntheticresinous fiber cloths are available. Among these may be mentioned: nylonfabric; fabrics woven from polyester filaments available under thetrademark Dacron; vinylidene chloride polymer screening available underthe trademark Saran; fabrics woven from acrylonitrile filamentsavailable under the trademark Orion; fabrics woven fromacrylonitrile-vinyl chloride copolymers available under the trademarksDynel and Vinylon, Type N; and the like. Perforated film and foraminousnonwoven fabric possessing the other requisite characteristics andhaving suitable porosity may also be used. Screen members having fromabout 400 to 6400 openings per square inch have been used. A preferredmaterial is nylon mesh having from about 2000 to 3000 openings persquare inch. In addition to synthetic resinous screens, metal screening(such as, for example, stainless steel) may also be used. The filterelement 34 when used The may be formed of similar mesh material,preferably somewhat finer than that of the screen members.

The manifold tube 28 is also preferably formed of synthetic resinousmaterial such as, for example: polyvinyl chloride; the transparenttubing sold under the trademark Tygon; trifiuorochloroethylene polymersavailable under the trademark Kel-F; tubing formed of vinylidenechloride polymers available under the trademark Saran; tubing made fromtetrafluoroethylene polymers and available under the trademark Teflonand the like.

In use the oxygenator of this invention is suspended vertically in asuitable supporting rack and held under four-way tension. Supportingrods 14, 16, 18 and 20 are inserted in their respective loo-p membersand tension is placed upon the rods in order to hold the oxygenatorenvelope taut. T he oxygenator is, of course, sterile at the time ofuse. The oxygen inlet 38 is connected to a suitable source of pureoxygen, preferably through a humidifier.

In a typical cardiac operation, as described in some detail in ourprevious applications, the patients heart is first exposed and the twolarge veins at the right side of the heart which return the body bloodto the heart are loosely looped with tape ready to be tied. Catheters tothe great veins of the heart are inserted through a slit in the rightatrium and a catheter to the systemic artery is inserted through atransected subclavian artery. The oxygenator is primed by pouring aquantity of whole arterial blood into the oxygenator envelope or byarterializing venous blood through the oxygenator and then admitting itinto the blood reservoir 42. The tube from the veins of the patientpasses through a standard blood pump and is connected to the blood inlettube 31 of the oxygena'tor. The blood discharge tube 43 is connectedthrough a similar standard blood pump to return the oxygenated blood tothe artery system of the patient.

With the oxygenator thus connected to the circulatory system of thepatient the blood pumps are turned on and the tapes looping the bloodvessels are tightened. The heart, still beating, empties of blood. Thevenous blood, instead of going through the heart and lungs, passesthrough the blood pump and into the blood inlet 31 of the oxygenator.Blood flows from the manifold 28 through the manifold openings 32 (intothe filter 34 when used) and into the narrow space 23 between the screenmembers 21 and 22. The openings 33 at the top of the manifold preventany airlock and any air or other gases escaping through the openings 33,pass out into the envelope from where they may escape through thedischarge vent 39.

The blood flowing down between the screen members 21 and 22 forms andmaintains a thin, substantially uniform film of blood. The surfacetension of the blood combined with the non-wetting characteristics ofthe screen and the positive gas pressure against the screen insuresagainst passage of any blood through the screen so that the only flow isdownward. The thickness of the blood film is determined and maintainedby the spacer elements inserted between the taut screen members. It hasbeen found that for adequate oxygenation the film thickness (andconsequently the screen spacing) should be maintained at between about0.015 and 0.045 of an inch and preferably between about 0.025 and 0.035of an inch.

As pure oxygen is introduced under pressure into the oxygenator envelopethrough the oxygen inlet tube 38 the space 40 is maintained under slightpositive pressure and there is a slight ballooning effect. The entirefilm of blood in the space 23 between the screen is thus in intimatecontact with oxygen under pressure through the multitudinous openings inthe screened member 21. The opposite side of the blood film is incontact with the space 41 through the multitudinous openings in thescreen 22 to permit escape of carbon dioxide from the oxygenated blood.The space 41 is likewise maintained under slight positive pressure. Theexcess oxygen from the oxygen inlet 38 sweeps through the space 40 inintimate contact with the blood film through the screen 21, through theplurality of vent openings 27 at the opposite side of the oxygenatorenvelope. It then sweeps out through the space 41 along the back face.of the blood film, carrying with it carbon dioxide displaced from theblood film, and escapes through the vent 39.

The oxygenated blood fiows downwardly through the space 23 between thescreens as a continuous film to the bottom of the oxygenator where it iscollected in the reservoir 42 and returned to the patient through theblood outlet tube 43. When the preferred form of oxygenatorconstruction,.as shown in Figure 1, is employed the oxygenated bloodflows from between the bottom of the oxygenator screens to the inclinedpassage 44 in which a downward laminar flow may take place. The heaviergas-free blood flows beneath and continuously displaces upwardlygas-containing blood of lesser density to liberate entrained gasbubbles, if any be present, and any such gas may then escape through thevent 45. This added safeguard may be used out of an abundance of cautionto insure against any gas emboli, but under usual circumstances andnormal operations no such added precaution should be necessary.

The oxygenator may, of course, be made in a variety of sizes inorder toprovide the oxygenating capacity required by patients of varying age andWeight groups from infants to adults. In order to standardizemanufacturing procedures, however, it is preferred that the oxygenatorbe made of a size having adequate oxygenating capacity for most infants,and then, when greater oxygenating capacity may be required, a pluralityof these standard size units connected in parallel may be used. Thus, asa typical example, the oxygenator may be constructed so as to have aneffective oxygenating screen surface of about 18 by 24 inches and asneed for greater capacity arises a plurality of two or more of suchstandard size units are used connected in parallel with each other.

A circulation system incorporating the oxygenator of this invention maybe provided with means for introducing supplemental venous blood asdescribed in our previous applications. Similarly, the coronary sinussuction device for returning cardiotomy loss to the patient through theoxygenator as disclosed in our previous applications may be utilized inconnection with the oxygenator of this invention.

It is apparent that many modifications and variations of this inventionas herernbefore set forth may be made without departing from the spiritand scope thereof. The specific embodiments described are given by wayof example only and the invention is limited only by the terms of theappended claims.

We claim:

1. A blood oxygenator comprising a pair of parallel spaced apartforaminous blood filming elements enclosed within an envelope, inletmeans for introducing oxygen into said envelope on one side of said pairof filming elements, gas discharge means for venting gases from saidenvelope on the other side of said pair of filming elements, blood inletmeans for introducing blood to be oxygenated between said pair offilming elements, said blood inlet means comprising a perforatedmanifold tube disposed adjacent to the top of said oxygenatorenvelopeand between said pair of blood filming elements, and outlet means fordischarging oxygenated blood from said envelope.

2. A blood oxygenator according to claim 1 further characterized in thatsaid pair of blood filming elements is composed of fine mesh wovenscreens.

3. A blood oxygenator according to claim 2 further characterized in thatsuch screens are composed of synthetic resinous filaments non-wettableby blood.

4. A blood oxygenator according to claim 1 further characterized in thatsaid blood filming elements are the Mechanical held substantiallyuniformally spaced apart by means of spacer elements between saidfilming elements.

5. A blood oxygenator according to claim 1 further characterized in thatsaid oxygen inlet means and said gas discharge means are disposedgenerally adjacent to one side edge of said oxygenator envelope inopposite faces thereof and gas passage means to permit flow of gasaround one side edge of said pair of filming elements are disposedwithin the envelope adjacent the side of the marginal edge of the pairof filming elements which is opposite thereto.

6. A blood oxygenator according to claim 1 further characterized in thatmeans are provided adjacent to the side edge portion of said oxygenatorfor supporting and tensioning said oxygenator to maintain the pair ofblood filming elements taut and substantially uniformally spaced apart.

7. A blood oxygenator according to claim 1 further characterized in thatoxygenator envelope is composed of thin, relatively transparent, heatsealable synthetic resinous film.

8. A blood oxygenator comprising a pair of parallel closely spaced apartforaminous blood filming elements composed of synthetic resinousfilaments woven into a fine mesh screen and enclosed within a generallytransparent synthetic resinous film envelope, oxygen inlet means in oneface of said envelope adjacent to one side edge thereof for introducingoxygen into said envelope on one side of said pair of filming elements,gas discharge means in the opposite face of said envelope adjacent tothe same side edge as the oxygen inlet for venting gases from saidenvelope on the other side of said pair of filming elements, a pluralityof gas passages within said envelope adjacent the side edge of said pairof filming elements opposite to said oxygeninlet and gas discharge,blood inlet means for introducing blood into the oxygenator between saidpair of filming elements, said blood inlet means including a perforatedmanifold tube disposed between said blood filming elements ad jacent thetop of the oxygenator envelope, spacer means between the oppositevertical side edges of said blood filming elements and between the upperportion thereof below said manifold tube, tensioning means adjacent themarginal edges of said oxygenator for applying tension thereto to holdthe blood filming elements taut and substantially uniformly spacedapart, and a blood outlet adjacent the bottom of said envelope fordischarging oxygenated blood from said envelope.

9. A blood oxygenator according to claim 8 further characterized in thatsaid outlet means includes an inclined passage extending from adjacentthe bottom of said pair of filming elements to a blood collectingreservoir, the top of said rservoir being open to the atmosphere topermit the escape of gases.

10. A blood oxygenator according to claim 8 further characterized inthat said filming elements are spaced apart between about 0.015 and0.045 of an inch.

11. A blood oxygenator according to claim 8 further characterized inthat said foraminous screen filming elements are provided with between400- and per square inch.

OTHER REFERENCES Recent Advances in the Development of Heart and LungApparatus Annals of Surgery, vol. 134, No. 4, October 1951, pp. 694-708(pp. 695-702 relied on).

Brown et al.: A Simple Expendable Blood Oxygen Gas Exchanger, Surgery,vol. 40, No. 1, July 1956, pp. -112' (pp. 100-103 relied on). (Availablein Science Library.) Y

Miller et al.:

6400 openings 4 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent N00 2 981 253 April 25 1961 Richard A., De Wall et a1 It ishereby certified that error appears in the above numbered patentrequiring correction and that the sai d Letters Patent should read ascorrected below.

Column 3 line 66 for Vinylon'" read me Vinyon Signed and sealed this19th day of September 1961 SEA L) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of PatentsUSCOM M-DC

